Default Constructors in Visual C#.NET

Printer QR-Code in Visual C#.NET Default Constructors
Default Constructors
QR Code 2d Barcode Encoder In C#.NET
Using Barcode generation for Visual Studio .NET Control to generate, create QR Code image in Visual Studio .NET applications.
It is important to note that by adding a constructor explicitly, you can no longer instantiate an Employee from within Main() without specifying the first and last names The code shown in Listing 518, therefore, will not compile
Barcode Encoder In C#
Using Barcode creator for .NET Control to generate, create barcode image in VS .NET applications.
Listing 518 Default Constructor No Longer Available
Making QR Code JIS X 0510 In Visual Studio .NET
Using Barcode encoder for ASP.NET Control to generate, create QR image in ASP.NET applications.
[View full width]
QR Code JIS X 0510 Printer In Visual Studio .NET
Using Barcode printer for .NET framework Control to generate, create QR-Code image in VS .NET applications.
class Program { static void Main() { Employee employee; // ERROR:No overload for method 'Employee' // takes '0' arguments //employee = new Employee();
Creating Denso QR Bar Code In VB.NET
Using Barcode printer for .NET Control to generate, create QR-Code image in Visual Studio .NET applications.
// } }
Paint Barcode In Visual C#
Using Barcode encoder for .NET Control to generate, create barcode image in Visual Studio .NET applications.
If a class has no explicitly defined constructor, then the C# compiler adds one during compilation This constructor takes no parameters and is, therefore, the default constructor by definition As soon as you add an explicit constructor to a class, the C# compiler no longer provides a default constructor Therefore, with Employee(string firstName, string lastName) defined, the default constructor, Employee(), is not added by the compiler You could explicitly add such a constructor, but then you would again be allowing construction of an Employee without specifying the employee name It is not necessary to rely on the default constructor defined by the compiler It is also possible for programmers to define a default constructor explicitly, perhaps one that initializes some fields to particular values Defining the default constructor simply involves declaring a constructor that takes no parameters
Bar Code Encoder In C#
Using Barcode creator for Visual Studio .NET Control to generate, create barcode image in .NET applications.
Advanced Topic: Finalizers
Code 3/9 Drawer In Visual C#.NET
Using Barcode printer for .NET Control to generate, create Code 3 of 9 image in VS .NET applications.
Constructors define what happens during the instantiation process of a class To define what happens when an object is destroyed C# provides the finalizer construct Unlike destructors in C++, finalizers do not run immediately after an object goes out of scope Rather, the finalizer executes after an object is last active and before the program shuts down Specifically, the garbage collector identifies objects with finalizers during a garbage collection cycle, and instead of immediately de-allocating those objects, it adds them to a finalization queue A separate thread runs through each object in the finalization queue and calls their finalizer before removing them from the queue and making them available for the garbage collector again 9 discusses this process, along with resource cleanup, in depth
Code 128 Code Set A Encoder In Visual C#
Using Barcode encoder for .NET framework Control to generate, create Code128 image in .NET framework applications.
Overloading Constructors
Print Data Matrix 2d Barcode In C#
Using Barcode creator for Visual Studio .NET Control to generate, create DataMatrix image in VS .NET applications.
Constructors can be overloaded For example, as Listing 519 shows, you could provide a constructor that has an employee ID with first and last names, or even just the employee ID
EAN / UCC - 13 Maker In .NET Framework
Using Barcode creation for Visual Studio .NET Control to generate, create GTIN - 13 image in VS .NET applications.
Listing 519 Overloading a Constructor
Making ECC200 In VB.NET
Using Barcode generator for .NET Control to generate, create ECC200 image in VS .NET applications.
class Employee { public Employee(string firstName, string lastName) { FirstName = firstName; LastName = lastName; } public Employee( int id, string firstName, string lastName ) { Id = id; FirstName = firstName; LastName = lastName; } public Employee(int id) { Id = id; // Look up employee name // } public public public public // } intId; string FirstName; string LastName; string Salary;
Generate Code-128 In VB.NET
Using Barcode maker for .NET Control to generate, create ANSI/AIM Code 128 image in Visual Studio .NET applications.
This enables ProgramMain() to instantiate an employee from the first and last names either by passing in the employee ID only, or by passing both the names and the IDs You would use the constructor with both the names and the IDs when creating a new employee in the system You would use the constructor with only the ID to load up the employee from a file or a database
Printing Bar Code In .NET Framework
Using Barcode drawer for VS .NET Control to generate, create bar code image in .NET framework applications.
Calling Another Constructor Using this
Printing Data Matrix 2d Barcode In Visual Studio .NET
Using Barcode generation for ASP.NET Control to generate, create Data Matrix image in ASP.NET applications.
Notice in Listing 519 that the initialization code for the Employee object is now duplicated in multiple places and, therefore, has to be maintained in multiple places The amount of code is small, but there are ways to eliminate the duplication by calling one constructor from another, using constructor initializers Constructor initializers determine which constructor to call before executing the implementation of the current constructor (see Listing 520)
Bar Code Printer In Java
Using Barcode generator for Java Control to generate, create barcode image in Java applications.
Listing 520 Calling One Constructor from Another
Creating Code 39 Extended In .NET
Using Barcode generator for Visual Studio .NET Control to generate, create Code-39 image in VS .NET applications.
class Employee { public Employee(string firstName, string lastName) { FirstName = firstName; LastName = lastName; } public Employee( int id, string firstName, string lastName ) : this(firstName, lastName) { Id = id; } public Employee(int id) { string firstName; string lastName; Id = id; // Look up employee name // } // NOTE:Member constructors cannot be // called explicitly inline // this(id, firstName, lastName);
Making Barcode In VS .NET
Using Barcode creation for .NET framework Control to generate, create bar code image in Visual Studio .NET applications.
public public public public // }
Printing Code 39 Extended In Visual Studio .NET
Using Barcode creator for ASP.NET Control to generate, create Code 39 Full ASCII image in ASP.NET applications.
int Id; string FirstName; string LastName; string Salary;
GS1-128 Encoder In Java
Using Barcode creation for Java Control to generate, create EAN 128 image in Java applications.
To call one constructor from another within the same class (for the same object instance) C# uses a colon followed by the this keyword followed by the parameter list on the callee constructor's declaration In this case, the constructor that takes all three parameters calls the constructor that takes two Often, the calling pattern is reversed; the constructor with the fewest parameters calls the constructor with the most parameters, passing defaults for the parameters that are not known